Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
  • C09C3/00—Treatment in general of inorganic materials, other than fibrous fillers, to enhance their pigmenting or filling properties
  • C09C3/10—Treatment with macromolecular organic compounds
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K8/00—Cosmetics or similar toiletry preparations
  • A61K8/18—Cosmetics or similar toiletry preparations characterised by the composition
  • A61K8/19—Cosmetics or similar toiletry preparations characterised by the composition containing inorganic ingredients
  • A61K8/27—Zinc; Compounds thereof
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K8/00—Cosmetics or similar toiletry preparations
  • A61K8/18—Cosmetics or similar toiletry preparations characterised by the composition
  • A61K8/72—Cosmetics or similar toiletry preparations characterised by the composition containing organic macromolecular compounds
  • A61K8/84—Cosmetics or similar toiletry preparations characterised by the composition containing organic macromolecular compounds obtained by reactions otherwise than those involving only carbon-carbon unsaturated bonds
  • A61K8/88—Polyamides
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61Q—SPECIFIC USE OF COSMETICS OR SIMILAR TOILETRY PREPARATIONS
  • A61Q17/00—Barrier preparations; Preparations brought into direct contact with the skin for affording protection against external influences, e.g. sunlight, X-rays or other harmful rays, corrosive materials, bacteria or insect stings
  • A61Q17/04—Topical preparations for affording protection against sunlight or other radiation; Topical sun tanning preparations
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y5/00—Nanobiotechnology or nanomedicine, e.g. protein engineering or drug delivery
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G49/00—Compounds of iron
  • C01G49/0018—Mixed oxides or hydroxides
  • C01G49/0072—Mixed oxides or hydroxides containing manganese
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G49/00—Compounds of iron
  • C01G49/02—Oxides; Hydroxides
  • C01G49/08—Ferroso-ferric oxide [Fe3O4]
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G9/00—Compounds of zinc
  • C01G9/02—Oxides; Hydroxides
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
  • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
  • C09C1/04—Compounds of zinc
  • C09C1/043—Zinc oxide
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
  • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
  • C09C1/22—Compounds of iron
  • C09C1/24—Oxides of iron
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K2800/00—Properties of cosmetic compositions or active ingredients thereof or formulation aids used therein and process related aspects
  • A61K2800/40—Chemical, physico-chemical or functional or structural properties of particular ingredients
  • A61K2800/41—Particular ingredients further characterized by their size
  • A61K2800/412—Microsized, i.e. having sizes between 0.1 and 100 microns
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K2800/00—Properties of cosmetic compositions or active ingredients thereof or formulation aids used therein and process related aspects
  • A61K2800/40—Chemical, physico-chemical or functional or structural properties of particular ingredients
  • A61K2800/41—Particular ingredients further characterized by their size
  • A61K2800/413—Nanosized, i.e. having sizes below 100 nm
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/60—Particles characterised by their size
  • C01P2004/64—Nanometer sized, i.e. from 1-100 nanometer
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2006/00—Physical properties of inorganic compounds
  • C01P2006/12—Surface area
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
  • Y10T428/2982—Particulate matter [e.g., sphere, flake, etc.]
  • Y10T428/2991—Coated
  • Y10T428/2998—Coated including synthetic resin or polymer

Definitions

• the present invention relates to powder compositions of surface-modified nanoparticulate particles of at least one metal oxide, metal hydroxide and/or metal oxide hydroxide, to a method for the production thereof and also to their use for cosmetic sunscreen preparations, as stabilizers in plastics and as antimicrobial active ingredient.
• the invention further relates to a method of producing aqueous suspensions of surface-modified nanoparticulate particles of at least one metal oxide, metal hydroxide and/or metal oxide hydroxide.
• Metal oxides are used for diverse purposes, thus, for example, as white pigment as catalyst as constituent of antibacterial skin protection ointments and as activator for the vulcanization of rubber. Finely divided zinc oxide or titanium dioxide is found as UV-absorbing pigments in cosmetic sunscreen compositions.
• nanoparticles refers to particles with an average diameter of from 5 to 10000 nm, determined by means of electron-microscopic methods.
• Zinc oxide nanoparticles with particle sizes below about 30 nm are potentially suitable for use as UV absorbers in transparent organic-inorganic hybrid materials, plastics, paints and coatings.
• a use for protecting UV-sensitive organic pigments is also possible.
• Particles, particle aggregates or particle agglomerates of zinc oxide which are larger than about 30 nm lead to scattered light effects and thus to an undesired decrease in transparency in the visible light region.
• the redispersibility i.e. the ability of the prepared zinc oxide nanoparticles to be converted to a colloidally disperse state, is therefore an important prerequisite for the abovementioned applications.
• Zinc oxide nanoparticies with particle sizes below about 5 nm exhibit, due to the quantum size effect, a blue shift of the absorption edge (L. Brus, J. Phys. Chem. (1986), 90, 2555-2560) and are therefore less suitable for use as UV absorbers in the UV-A region.
• metal oxides for example of zinc oxide by dry and wet methods
• the classic method of burning zinc which is known as a dry method (e.g. Gmelin vol. 32, 8th edition, supplementary volume, p. 772 ff.), produces aggregated particles with a broad size distribution.
• a dry method e.g. Gmelin vol. 32, 8th edition, supplementary volume, p. 772 ff.
• Particularly finely divided zinc oxide is produced primarily wet-chemically by precipitation processes.
• the precipitation in aqueous solution generally produces hydroxide- and/or carbonate-containing materials which have to be converted thermally to zinc oxide.
• the thermal treatment has an adverse effect on the finely divided nature since the particles are here subjected to sintering processes which lead to the formation of micrometer-sized aggregates which can only be broken down incompletely to the primary particles by grinding.
• Nanoparticulate metal oxides can be obtained, for example, by the microemulsion method.
• a solution of a metal alkoxide is added dropwise to a water-in-oil microemulsion.
• the hydrolysis of the alkoxides to the nanoparticulate metal oxide then takes place.
• the disadvantages of this process are, in particular, that the metal oxides are expensive starting materials, that emulsifiers have to additionally be used and that the production of the emulsions with droplet sizes in the nanometer range is a complex process step.
• WO 00/50503 describes zinc oxide gels which comprise nanoparticutate zinc oxide particles with a particle diameter of ⁇ 15 nm and which are redispersible to give sols.
• the precipitates produced by basic hydrolysis of a zinc compound in alcohol or in an alcohol/water mixture are redispersed by adding dichloromethane or chloroform.
• a disadvantage here is that in water or in aqueous dispersants, stable dispersions are not obtained.
• WO 93/21127 describes a method of producing surface-modified nanoparticulate ceramic powders.
• a nanoparticulate ceramic powder is surface-modified by applying a low molecular weight organic compound, for example propionic acid.
• This method can not be used for the surface modification of zinc oxide since the modification reactions are carried out in aqueous solution and zinc oxide dissolves in aqueous organic acids.
• This method can therefore not be used for producing zinc oxide dispersions; moreover, in this application, zinc oxide is also not specified as a possible starting material for nanoparticulate ceramic powders.
• JP-A-04 164 814 describes a method which leads to finely divided zinc oxide by precipitation in aqueous medium at elevated temperature even without a subsequent thermal treatment.
• the average particle size stated is 20-50 nm with no indication of the degree of agglomeration. These particles are relatively large. Even if agglomeration is minimal, this leads to scatter effects which are undesired in transparent applications.
• JP-A-07 232 919 describes the production of zinc oxide particles of 5 to 10000 nm in size from zinc compounds through reaction with organic acids and other organic compounds, such as alcohols, at elevated temperature.
• the hydrolysis occurs here such that the formed by-products (esters of the acids used) can be distilled off.
• the method allows the production of zinc oxide powders which are redispersible by virtue of prior surface modification.
• it is not possible to produce particles with an average diameter of ⁇ 15 nm. Accordingly, in the examples listed in the application, 15 nm is specified as the smallest average primary particle diameter.
• Metal oxides that are hydrophobized with organosilicon compounds are described, inter alia, in DE 33 14 741 A1, DE 36 42 794 A1 and EP 0 603 627 A1 and also in WO 97/16156.
• the object of the present invention was therefore to provide nanoparticulate metal oxides, metal hydroxides and/or metal oxide hydroxides which allow the production of stable nanoparticulate dispersions in water or polar organic solvents and also in cosmetic oils. Irreversible aggregation of the particles should be avoided if possible so that a complex grinding process can be avoided.
• This object was achieved by a method of producing an aqueous suspension of surface-modified nanoparticulate particles of at least one metal oxide, metal hydroxide and/or metal oxide hydroxide, where the metal or metals are chosen from the group consisting of aluminum, magnesium, cerium, iron, manganese, cobalt, nickel, titanium, zinc and zirconium, wherein
• the metal oxide, metal hydroxide and metal oxide hydroxide can here either be the anhydrous compounds or the corresponding hydrates.
• the metal salts in process step a) may be metal halides, acetates, sulfates or nitrates.
• Preferred metal salts here are halides, for example zinc chloride or titanium tetrachloride, acetates, for example zinc acetate, and also nitrates, for example zinc nitrate.
• a particularly preferred metal salt is zinc nitrate or zinc acetate.
• the polymers may be, for example, polyaspartic acid, polyvinylpyrrolidone or copolymers of an N-vinylamide, for example N-vinylpyrrolidone, and at least one further monomer comprising a polymerizable group, for example with monoethylenically unsaturated C 3 -C 8 -carboxylic acids, such as acrylic acid, methacrylic acid, C 8 -C 30 -alkyl esters of monoethylenically unsaturated C 3 -C 8 -carboxylic acids, vinyl esters of aliphatic C 8 -C 30 -carboxylic acids and/or with N-alkyl- or N,N-dialkyl-substituted amides of acrylic acid or of methacrylic acid with C 8 -C 18 -alkyl radicals.
• monoethylenically unsaturated C 3 -C 8 -carboxylic acids such as acrylic acid, methacrylic acid,
• a preferred embodiment of the method according to the invention is one in which the precipitation of the metal oxide, metal hydroxide and/or of the metal oxide hydroxide takes place in the presence of polyaspartic acid.
• polyaspartic acid comprises both the free acid and also the salts of polyaspartic acid, such as, for example, sodium, potassium, lithium, magnesium, calcium, ammonium, alkylammonium, zinc and iron salts or mixtures thereof.
• a particularly preferred embodiment of the method according to the invention is one in which polyaspartic acid, in particular the sodium salt of polyaspartic acid having an average molecular weight of from 500 to 1000000, preferably 1000 to 20000, particularly preferably 1000 to 8000, very particularly preferably 3000 to 7000, determined by gel-chromatographic analysis, is used.
• polyaspartic acid in particular the sodium salt of polyaspartic acid having an average molecular weight of from 500 to 1000000, preferably 1000 to 20000, particularly preferably 1000 to 8000, very particularly preferably 3000 to 7000, determined by gel-chromatographic analysis, is used.
• the two solutions are mixed in process step a) at a temperature T 1 in the range from 0° C. to 50° C., preferably in the range from 15° C. to 40° C., particularly preferably in the range from 15° C. to 30° C.
• the mixing can be carried out at a pH value in the range from 3 to 13.
• the pH value during mixing is in the range from 7 to 11.
• the time for mixing the two solutions in process step a) is preferably in the range from 0.5 to 30 minutes, particularly preferably in the range from 0.5 to 10 minutes.
• the mixing in process step a) can be done, for example, through the metered addition of the aqueous solution of a metal salt, for example of zinc acetate or zinc nitrate to an aqueous solution of a mixture of polyaspartic acid and an alkali metal hydroxide or ammonium hydroxide, in particular sodium hydroxide, or through simultaneous metered addition in each case of an aqueous solution of a metal salt and an aqueous solution of an alkali metal hydroxide or ammonium hydroxide to give an aqueous polyaspartic acid solution.
• a metal salt for example of zinc acetate or zinc nitrate
• an alkali metal hydroxide or ammonium hydroxide in particular sodium hydroxide
• the temperature T 2 in process step b) is in the range from 60 to 300° C., preferably in the range from 70 to 150° C., particularly preferably in the range from 80 to 100° C.
• the residence time of the mixture in the temperature T 2 chosen in process step b) is 0.1 to 30 minutes, preferably 0.5 to 10 minutes, particularly preferably 0.5 to 5 minutes.
• the heating from T 1 to T 2 occurs within 0.1 to 5 minutes, preferably within 0.1 to 1 minute, particularly preferably within 0.1 to 0.5 minutes.
• a further preferred embodiment of the method according to the invention is one in which the process steps a) and/or b) take place continuously.
• the method is preferably carried out in a tubular reactor.
• the method is carried out in a way in which
• the methods described previously are particularly suitable for producing an aqueous suspension of surface-modified nanoparticulate particles of titanium dioxide and zinc oxide, in particular of zinc oxide.
• the precipitation of the surface-modified nanoparticulate particles of zinc oxide from an aqueous solution of zinc acetate, zinc chloride or zinc nitrate takes place at a pH value in the range from 7 to 11 in the presence of polyaspartic acid having an average molecular weight of from 1000 to 8000.
• a further advantageous embodiment of the method according to the invention is one in which the surface-modified nanoparticulate particles of a metal oxide, metal hydroxide and/or metal oxide hydroxide, in particular of zinc oxide, have a BET surface area in the range from 25 to 500 m 2 /g, preferably 30 to 400 m 2 /g, particularly preferably 40 to 300 m 2 /g, very particularly preferably 50 to 250 m 2 /g.
• the invention is based on the finding that, through a surface modification of nanoparticulate metal oxides, metal hydroxides and/or metal oxide hydroxides with polyaspartic acid and/or salts thereof, it is possible to achieve a long-term stability of dispersions of the surface-modified metal oxides, in particular in cosmetic preparations, without undesired pH changes during the storage of these preparations.
• the invention further provides a method of producing a powder composition of surface-modified nanoparticulate particles of at least one metal oxide, metal hydroxide and/or metal oxide hydroxide, where the metal or metals are chosen from the group consisting of aluminum, magnesium, cerium, iron, manganese, cobalt, nickel, titanium, zinc and zirconium, wherein
• the precipitated particles can be separated from the aqueous reaction mixture in process step c) in a manner known per se, for example by filtration or centrifugation.
• the filter cake obtained can be dried in a manner known per se, for example in a drying oven at temperatures between 40 and 100° C., preferably between 50 and 70° C. under atmospheric pressure, to constant weight.
• the present invention further provides powder compositions of surface-modified nanoparticulate particles of at least one metal oxide, metal hydroxide and/or metal oxide hydroxide, where the metal or metals are chosen from the group consisting of aluminum, magnesium, cerium, iron, titanium, manganese, cobalt, nickel, zinc and zirconium, and the surface modification comprises a coating with at least one polymer, obtainable by the methods described at the start.
• the present invention further provides powder compositions of surface-modified nanoparticulate particles of at least one metal oxide, metal hydroxide and/or metal oxide hydroxide, in particular of zinc oxide, where the surface modification comprises a coating with polyaspartic acid, having a BET surface area in the range from 25 to 500 m 2 /g, preferably 30 to 400 m 2 /g, particularly preferably 40 to 300 m 2 /g, very particularly preferably 50 to 250 m 2 /g.
• the present invention further provides the use of powder compositions of surface-modified nanoparticulate particles of at least one metal oxide, metal hydroxide and/or metal oxide hydroxide, in particular titanium dioxide or zinc oxide, which are produced by the method according to the invention, for example
• the surface-modified nanoparticulate particles of at least one metal oxide, metal hydroxide and/or metal oxide hydroxide, in particular titanium dioxide or zinc oxide are redispersible in a liquid medium and forms stable dispersions. This is particularly advantageous because, for example, the dispersions produced from the zinc oxide according to the invention do not have to be dispersed again prior to further processing, but can be processed directly.
• the surface-modified nanoparticulate particles of at least one metal oxide, metal hydroxide and/or metal oxide hydroxide are redispersible in polar organic solvents and forms stable dispersions. This is particularly advantageous since, as a result of this, uniform incorporation for example into plastics or films is possible.
• the surface-modified nanoparticulate particles of at least one metal oxide, metal hydroxide and/or metal oxide hydroxide are redispersible in water, where it forms stable dispersions. This is particularly advantageous since this opens up the possibility of using the material according to the invention, for example, in cosmetic formulations, where the omission of organic solvents constitutes a major advantage. Also conceivable are mixtures of water and polar organic solvents.
• the surface-modified nanoparticulate particles have a diameter of from 10 to 200 nm. This is particularly advantageous since good redispersibility is ensured within this size distribution.
• the surface-modified nanoparticulate particles have a diameter of from 10 to 50 nm.
• This size range is particularly advantageous since, for example, following redispersion of such zinc oxide nanoparticles, the dispersions which form are transparent and thus do not influence the coloring, for example, when added to cosmetic formulations. Moreover, this also gives rise to the possibility of use in transparent films.
• Solution A comprised 43.68 g of zinc acetate dihydrate per liter and had a zinc concentration of 0.2 mol/l.
• Solution B comprised 16 g of sodium hydroxide per liter and thus had a sodium hydroxide concentration of 0.4 mol/l. Moreover, solution B also comprised 20 g/l of sodium polyaspartate.
• the suspension obtained then flowed through a second heat exchanger in which the suspension was kept at 85° C. for a further 30 seconds.
• the suspension then flowed successively through a third and fourth heat exchanger in which the suspension was cooled to room temperature within a further minute.
• the suspension obtained was collected in drums.
• the resulting powder had, in the UV-VIS spectrum, the absorption band characteristic of zinc oxide at about 350-360 nm.
• the X-ray diffraction of the powder displayed exclusively the diffraction reflections of hexagonal zinc oxide.
• the half-width of the X-ray reflections was used to calculate a crystallite size, which is between 8 nm [For the (102) reflection] and 37 nm [for the (002) reflection].
• Measurement of the particle size distribution by means of laser diffraction led to a monomodal particle size distribution.
• the specific BET surface area was 42 m 2 /g.
• SEM scanning electron microscope
• TEM transmission electron microscopy
• the powder obtained had an average particle size of from 50 to 100 nm.
• the TEM micrograph showed that the zinc oxide particles have a very high porosity and consist of very small primary particles with a diameter of 5-10 nm.
• a suspension stream was pumped off from the resulting suspension via a riser pipe at 0.96/min and heated to a temperature of 85° C. in a downstream heat exchanger over the course of 1 minute.
• the resulting suspension then flowed through a second heat exchanger in which the suspension was kept at 85° C. for a further 30 seconds.
• the suspension then successively flowed through a third and fourth heat exchanger in which the suspension was cooled to room temperature over the course of a further minute.
• the resulting suspension was collected in drums.
• the product obtained had, in the UV-VIS spectrum, the absorption band characteristic of zinc oxide at about 350-360 nm.
• the X-ray diffraction of the powder exhibited exclusively the diffraction reflections of hexagonal zinc oxide.
• the half-width of the X-ray reflections was used to calculate a crystallite size, which is between 8 nm [for the (102) reflection] and 37 nm [for the (002) reflection].
• Measurement of the particle size distribution by means of laser diffraction led to a monomodal particle size distribution.
• the specific BET surface area was 42 m 2 /g.
• SEM scanning electron microscope
• TEM transmission electron microscopy
• the powder obtained had an average particle size of from 50 to 100 nm.
• the TEM micrograph showed that the zinc oxide particles have a very high porosity and consist of very small primary particles having a diameter of 5-10 nm.
• Solution C comprised 41.67 g of zinc acetate dehydrate and 2.78 g of iron(II) sulfate heptahydrate per liter and had a zinc concentration of 0.19 mol/l and an iron(II) concentration of 0.01 mol/l.
• Solution D comprised 16 g of sodium hydroxide per liter and thus had a sodium hydroxide concentration of 0.4 mol/l. Moreover, solution D also comprised 5 g/l of sodium polyaspartate.
• the resulting powder had, in the UV-VIS spectrum, the absorption band characteristic of zinc oxide at about 350-360 nm.
• the X-ray diffraction of the powder displayed exclusively the diffraction reflections of hexagonal zinc oxide with somewhat larger lattice parameters compared to nondoped zinc oxide.
• SEM scanning electron microscope
• TEM transmission electron microscopy
• the powder obtained had an average particle size of from 50 to 100 nm.
• the TEM micrograph showed that the zinc-iron oxide particles of the formula Zn 0.95 Fe 0.05 O have a very high porosity and consist of very small primary particles with a diameter of 5-10 nm.
• Energy-dispersive X-ray analysis (EDX) confirmed homogeneous distribution of zinc ions and iron ions in the sample.
• the powder obtained had, in the UV-VIS spectrum, the absorption band characteristic of zinc oxide at about 350-360 nm. In agreement with this, the X-ray diffraction of the powder exhibited exclusively the diffraction reflections of hexagonal zinc oxide with somewhat larger lattice parameters compared to nondoped zinc oxide. In the scanning electron microscope (SEM) and likewise in transmission electron microscopy (TEM), the powder obtained had an average particle size of from 50 to 100 nm. Moreover, the TEM micrograph showed that the zinc-iron oxide particles of the formula Zn 0.95 Fe 0.05 O have a very high porosity and consist of very small primary particles having a diameter of 5-10 nm. Energy-dispersive X-ray analysis (EDX) confirmed homogeneous distribution of zinc ions and iron ions in the sample.
• EDX Energy-dispersive X-ray analysis
• Solution E comprised 55.60 g of iron(II) sulfate heptahydrate and 101.59 g of iron(III) sulfate hexahydrate per liter and had an iron(II) concentration of 0.2 mol/l and an iron(III) concentration of 0.4 mol/l.
• Solution F comprised 70.4 g of sodium hydroxide per liter and thus had a sodium hydroxide concentration of 1.76 mol/l. Moreover, solution F also comprised 5 g/l of sodium polyaspartate.
• the X-ray diffraction of the resulting black powder displayed exclusively the diffraction reflections of cubic iron oxide of the formula Fe 3 O 4 .
• the half-width of the X-ray reflections was used to calculate a crystallite size of about 10 nm.
• the powder obtained had an average particle size of from 5 to 15 nm.
• the X-ray diffraction of the resulting black powder displayed exclusively the diffraction reflections of cubic iron oxide of the formula Fe 3 O 4 .
• the half-width of the X-ray reflections was used to calculate a crystallite size of about 10 nm.
• the powder obtained had an average particle size of from 5 to 15 nm.
• Solution G comprised 33.80 g of manganese(II) sulfate monohydrate and 101.59 g of iron(III) sulfate hexahydrate per liter and had a manganese(II) concentration of 0.2 mol/l and an iron(III) concentration of 0.4 mol/l.
• Solution H comprised 70.4 g of sodium hydroxide per liter and thus had a sodium hydroxide concentration of 1.76 mol/l. Moreover, solution H also comprised 5 g/l of sodium polyaspartate.
• the X-ray diffraction of the resulting black powder displayed exclusively the diffraction reflections of cubic manganese-iron oxide of the formula MnFe 2 O 4 .
• the half-width of the X-ray reflections were used to calculate a crystallite size of about 10 nm.
• TEM transmission electron microscopy
• the powder obtained had an average particle size of from 5 to 15 nm.
• the X-ray diffraction of the resulting black powder displayed exclusively the diffraction reflections of cubic manganese-iron oxide of the formula MnFe 2 O 4 .
• the half-width of the X-ray reflections was used to calculate a crystallite size of about 10 nm.
• TEM transmission electron microscopy
• the powder obtained had an average particle size of from 5 to 15 nm.
• Solution I comprised 30.42 g of manganese(II) sulfate monohydrate, 3.59 g of zinc sulfate monohydrate and 101.59 g of iron(III) sulfate hexahydrate per liter and had a manganese(II) concentration of 0.18 mol/l, a zinc concentration of 0.02 mol/l and an iron(III) concentration of 0.4 mol/l.
• Solution J comprised 70.4 g of sodium hydroxide per liter and thus had a sodium hydroxide concentration of 1.76 mol/l. Moreover, solution J also comprised 5 g/l of sodium polyaspartate.
• the X-ray diffraction of the resulting black powder displayed exclusively the diffraction reflections of cubic manganese-iron oxide of the formula MnFe 2 O 4 with somewhat smaller lattice parameters compared to nondoped MnFe 2 O 4 .
• the half-width of the X-ray reflections was used to calculate a crystallite size of about 10 nm.
• TEM transmission electron microscopy
• the powder obtained had an average particle size of from 5 to 15 nm.
• Energy-dispersive X-ray analysis (EDX) confirmed homogeneous distribution of manganese ions, zinc ions and iron ions in the sample.
• the X-ray diffraction of the resulting black powder displayed exclusively the diffraction reflections of cubic manganese-iron oxide of the formula MnFe 2 O 4 with somewhat smaller lattice parameters compared to nondoped MnFe 2 O 4 .
• the half-width of the X-ray reflections was used to calculate a crystallite size of about 10 nm.
• TEM transmission electron microscopy
• the powder obtained had an average particle size of from 5 to 15 nm.
• Energy-dispersive X-ray analysis (EDX) confirmed homogeneous distribution of manganese ions, zinc ions and iron ions in the sample.
• Solution K comprised 52.57 g of nickel(II) sulfate hexahydrate and 101.59 g of iron(III) sulfate hexahydrate per liter and had a nickel(II) concentration of 0.2 mol/l and an iron(111) concentration of 0.4 mol/l.
• Solution L comprised 70.4 g of sodium hydroxide per liter and thus had a sodium hydroxide concentration of 1.76 mol/l. Moreover, solution L also comprised 5 g/l of sodium polyaspartate.
• the X-ray diffraction of the resulting black powder displayed exclusively the diffraction reflections of cubic nickel-iron oxide of the formula NiFe 2 O 4 .
• the half-width of the X-ray reflections was used to calculate a crystallite size of about 10 nm, In transmission electron microscopy (TEM), the powder obtained had an average particle size of from 5 to 15 nm.
• Solution M comprised 47.31 g of nickel(II) sulfate hexahydrate, 3.59 g of zinc sulfate monohydrate and 101.59 g of iron(III) sulfate hexahydrate per liter and had a nickel(II) concentration of 0.18 mol/l, a zinc concentration of 0.02 mol/l and an iron(III) concentration of 04 mol/l.
• Solution N comprised 70.4 g of sodium hydroxide per liter and thus had a sodium hydroxide concentration of 1.76 mol/l. Moreover, solution N also comprised 5 g/l of sodium polyaspartate.
• the X-ray diffraction of the resulting black powder displayed exclusively the diffraction reflections of cubic nickel-iron oxide of the formula NiFe 2 O 4 with somewhat smaller lattice parameters compared to nondoped NiFe 2 O 4 .
• the half-width of the X-ray reflections was used to calculate a crystallite size of about 10 nm.
• TEM transmission electron microscopy
• the powder obtained had an average particle size of from 5 to 15 nm.
• Energy-dispersive X-ray analysis (EDX) confirmed homogeneous distribution of nickel ions, zinc ions and iron ions in the sample.
• the X-ray diffraction of the resulting black powder displayed exclusively the diffraction reflections of cubic nickel-iron oxide of the formula NiFe 2 O 4 with somewhat smaller lattice parameters compared to nondoped NiFe 2 O 4
• the half-width of the X-ray reflections was used to calculate a crystallite size of about 10 nm.
• TEM transmission electron microscopy
• the powder obtained had an average particle size of from 5 to 15 nm.
• Energy-dispersive X-ray analysis (EDX) confirmed homogeneous distribution of nickel ions, zinc ions and iron ions in the sample.

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